Preparation of transformer oils



United States Patent 3,192,153 EREPARATION QFTRANSFQRMER QELS Michael T. Smilslri, Mantua Township, Gloucester County, Nah, assignor to Socony Mobil Oil 6on1- pany, Inn, a corporation of New York 7 No Drawing. Filed Nov. 6, 1062, Ser. No. 235,847 4 Claims. (Ell. 200-264) This application is a continuation-in-part of application 145,776, filed October 17, 1961, now abandoned.

I This invention relates to the preparation of improved transformer oils. More specifically, this invention relates to the preparation of transformer oils which have improved non-sludging and electrical characteristics by hydrogenation of a specific hydrocarbon oil distillate.

The preparation of transformer oils for use in providing electrical insulation and conducting heat away from the transformer requires a careful and exacting procedure to provide a highly refined oil which requires a high dielectric strength, high electrical resistivity, low viscosity, low specific gravity, low pour test, non-emulsifying tendency, low evaporation rate, slow rate of sludge and/0r acid development by oxidation. The processes generally used to produce transformer oils include the multi-step procedure of acid treating or solvent refining of specific hydrocarbon oil distillates followed by clay percolation. These multi-step refining procedures, especially acid treating, are expensive to operate, waste oil and are associated with corrosion and pollution problems.

It is an object of this invention to provide an economical and commercially feasible one-step process to produce improve-d transformer oils. A further object of this invention is to provide improved transformer oils which have the superior physical characteristics of improved electrical insulatin g properties, reduced sludge forming tendencies, and possess other satisfactory properties required of commercial transformer oils such as oxidation resistance, low moisture formation, low acid production and the like. These and other objects will become apparent to those skilled in the art from a consideration of the following disclosure and appended claims.

In accordance with the present invention, improved transformer oils are produced by the treatment of a hydrocarbon oil distillate having a sulfur content below about 1 weight percent, preferably below about 0.7 weight percent, a viscosity at 100 F. of between about 35 and 110 S.S.U. and a flash point of between about 200 and 350 F. with hydrogen in the presence of a hydrogenation catalyst utilizing specific reaction conditions. The starting material which is utilized in the process of this invention can be a hydrocarbon oil distillate obtained from any available crude naphthenic petroleum oil. These hydrocarbon oil dist-illates can be obtained by vacuum distillation or like distillation of naphthenic crude oils such as Mirando, Webster, Thompson, Gulf Coast, among others. It is essential, however, that the hydrocarbon oil distillate used as the starting material has aviscosity range at 100 F. of about 35 to about 110 S.S.U., preferably in the range of about 54 to about 64 S.S.U.', a flash point in the range from about 200 to about 350 F., preferably a minimum flash point of about 270 F., and a pour point below about 50 F. One' of the requirements of a suitable transformer oil is a low pour point below about -50 F. Selection of the starting hydrocarbon oil distillates containing a high content of naphthenes and some aromatics will generally provide an oil which will satisfactorily meet the low pour point requirements. These naphthenic hydrocarbon oil distillates may contain naphthemes as low as 30 volume percent to 80 percent or higher.

An additional requirement of the naphthenic hydrocarbon distillate charge stock relates to the sulfur content therein. If the naphthenic hydrocarbon distillates have a sulfur content of 1 weight percent or higher, the improved transformer oil produced by the process of this invention is not obtained. If the naphthenic hydrocarbon distillates have a sulfur content below 1 weight percent, preferably below about 0.7 weight percent, an improved transformer oil is obtained utilizing the process of this invention.

The reaction conditions necessary for the production of improved transformer oils include a temperature range from about 600 F. to about 750 F. If a temperature below 600 F. or above 750 F. is employed, the resulting oil does not contain the desired improvements characteristic of an excellent transformer oil. The pressures which are employed include those above about 2000 pounds per square inch, preferably in the range from about 2000 to about 4000 pounds per square inch. Pressures above 4000 pounds persquare inch can be employed but are not commercially attractive since they are costly to produce and maintain and do not result in much, if any, improvement in yields and product quality. At pressures below about 2000 pounds per square inch, improved transformer oils are not obtained. The liquid hourly space velocities which can be used range from about 0.25 to about 2.0, preferably in the range from about 0.5 to about 1.5.

The catalysts employed in the process of this invention can include any type of catalyst having hydrogenation properties. Such catalysts are known in the art. For instance, these catalysts can include oxides and sulfides of any metal of Group Vl left-hand column of the Periodic System or mixtures thereof such as chromium sulfide, molybdenum sulfide, tungsten sulfide, and the like, sulfides of Group Vlll of the Periodic Table or. mixtures thereof such as the sulfides of iron, cobalt, nickel, platinum, palladium, rhodium, osmium, iridium, mixtures of the above sulfides of the metals of Group VI left-hand column and Group VIII such as a mixture of nickel sulfide and tungsten sulfide, tungsten sufide and cobalt sulfide, nickel sulfide and molybdenum sulfide and the like. These metals can be deposited on absorbent carriers such as alumina, silica-alumina, silica-Zirconia, among others. Preferred hydrogenation catalysts include 1:1 mol ratio mixture of nickel sulfide and tungsten sulfide; tungsten sulfide; and cobalt moly'odate supported or unsupported.

Pure hydrogen can be used in this process. Hydrogen of lower purity obtained by recycle from naphtha re forming or other hydrogenating processes can be used but it is recommended that the recycle hydrogen be subjected to a purification process to remove some of the undesirable impurities such as water, sulfur compounds and the like and maintain a high partial hydrogen pressure. Hydrogen can be circulated at a ratio in the range from about 500 to about 15,000 s.c.f. per barrel of charge, preferably in the range of about 1000 to about 2000 s.c.f. per barrel of charge, and if desired, higher or lower amounts can be used;

The process of this invention can be carried out in any equipment suitable for catalytic hydrogenation operations. The process may be operated batchwise. it is preferable, however, and generally more feasible to opcrate continuously. Accordingly, the process can be adapted to operations using a fixed bed of catalyst. Also, the process can be operated using a moving bed of catalyst, wherein the hydrocarbon flow can be concurrent or countercurrent to the catalyst flow. A fluid type-of operation can also be employed.

Important advantages are apparent in using the process of this invention over the conventional acid treatment and furfural refining procedures in producing transformer oils. Of significant importance, higher yields are obtained in the process of this invention over the conventional refining procedures since the charge stock is hydrogenated and converts the undesirable material into acceptable products. thereby utilizing the entire charge stock to produce the improved transformer oil which is taken directly from the reactor without further fractionation other than removal of gases such as hydrogen and hydrogen. sulfide. The acid treating and furfural refining procedure removes the undesirable material from the charge stock decreasing the yield of the resulting product and then requires an additional step of clay percolation to provide an acceptable transformer oil. Not only are higher yields obtained in less steps in'this invention, but transformer oils are produced which have improved characteristics for pro'viding more electrical insulation and reduced sludge accumulation over the conventional transformer oils. The following examples will serve to illustrate the process and improved products of the invent-ion without limiting the same:

EXAMPLE 1 Gulf (Grade A) coastal crude oil was distilled to obtain a transformer oil distillate having the following properties:

Gravity, API 26.3 Pour point F. -65 Flash point, F. 285 Viscosity, S.S.U. 100 F 57.0 Color, ASTM 4 /2 Neutralization number, mg. KOH/ gm. 0.86 Sulfur, percent wt. 0.17

Refractive index 1.49067 Molecular wt. 257

EXAMPLE 2 To compare the properties of a conventional transformer oil with a hydrogenated transformer oil, the starting material, similar to that described in Example 1, was acid treated with sulfuric acid using conventional procedures and the resulting product was'percolated through clay in order to obtain transformeroil which meets standard specifications. The starting material had the following properties:

Gravity, .API 26.3 Pour point F. 65 Flash point, F. 285 Viscosity, S.S.U. 100 F 57.0 Color, ASTM 4 /2 Neutralization number, mg. KOH/gm. 0.86 Sulfur, percent wt. 0.17

Refractive index 1.49067 Molecular wt. 257

The refined transformer oils had the following properties:

EXAMPLE 3 To compare the properties of a conventional transformer oil with a hydrogenated transformer oil, the starting material, similar to that described in Example 1, above, was refined 'by solvent extraction with furfural using a conventional procedure and the resulting product was percolated through clay in order to obtain transformer oil which vmeets standard specifications. The

starting material had the following properties:

Gravity, API 26.3 Pourpoint, F 65 Flash point, F 28'5 Viscosity, S.S.U. 100 F 57.0

Color, ASTM 4 /2 Neutralization number, mg. KOH/gm 0.86 Sulfur, percent wt 0.17 Refractive index 1.49067 Molecular wt 257 The refined transformer oils had the following properties:

Gravity, AP-I 30.0 Pour point, F. -65 Flash point, F. 2 Viscosity, S.S.U. 100 F 55.2 Color, ASTM 1 Neutralization number, mg. KOH/ gm 0.03 Sulfur, percent-wt 0.06 Refractive index 1.47655 Molecular wt. 285

EXAMPLE 4 'A portion of the transformer oil distillate of Example 1 was hydrogenated in the presence of a nickel-tungsten sulfide catalyst having the following composition and properties:

The reaction conditions were '500'F., a 0.25 liquid hourly space velocity, a hydrogen circulation ratio of 10,000 s.c.f. of hydrogen per barrel of charge stock, and a pressure of 1600 pounds per square inch. The transformer oil obtained had the following properties:

Gravity, API 27.7 Pour point, F. 65 Flash point F. 290 Viscosity, S.S.U. 100 F. 58.0 Color, ASTM 1- Neutralization number, mg. KOH/ gm. 0.01 Sulfur, percent wt. 0.028 Refractive index 1.48501 Molecular wt. 240

EXAMPLE 5 A portion of the transformer oil distillate of Example 1 was hydrogenated in the presence of nickel-tungsten sulfide catalyst, described in Example 4. The reaction conditions were 650 F., a 1.0 liquid hourly space velocity, a hydrogen circulation ratio of 2000 s.c.f. of hydrogen per barrel of charge stock and a pressure of 3000 pounds per square inch. The transformer oil obtained had the following properties:

Gravity, API 29.1 Pour point, F. 65 Flash point, F 2 Viscosity, S.S.U. F. 54.3 Color, ASTM 1- Neutralization number, mg. KOH/grn 0.01 Sulfur, percent wt 0.008 Refractive index 1.47783 Molecular wt.

EXAMPLE 6 To demonstrate the effect of sulfur, a transformer oil distillate having a sulfur content of 1 weight percent was hydrogenatedin the, presence of a nickel-tungsten sulfide catalyst described in Example 4. Reaction conditions were identical to the reaction conditions of Example 5; namely, 650 F., a 1.0 liquid hourly space Velocity, a hydrogen circulation ratio of 2000 s.c.f. of hydrogen per bar- 6 The resistivity of a transformer oil indicates the oiis ability to provide electrical insulation which is a primary function of a transformer oil. The transformer oil of this invention provides from about 3 to about 7 times more 4 times greater than the transformer oils of this invention.

rel of charge stock and a pressure of 3000 pounds per 5 electrical resistivity than the conventional oils. At the square inch. same time, the improved transformer oil of this inven- The naphthenic hydrocarbon distillate charge stock had tion meets the required specification for oxidation tendthe following properties: encies of an excellent transformer oil and is superior in Gravity e API 273 oxidation resistance over the furfural refined transformer o 01 $21 835; o g 1 38 The transformer oil of Example 4 hydrogenated under viscosity, o conditions outside the range of the condit ons of the Color, ASTM 31/2 process provides an acceptable transformer 011 according Neutralization number, mg KOH/grm L60 to spec fications but is only super or to the conventional Sulfur percent Wt. L0 0118 111 its ability to mamtarn a slightly lower sludge ac- Refractive index umulauon. Comparison of the milder hydrogenated 011 With the improved transformer oil of Example 5 indi- The trensfoh'hel on obtained from the hydrogenation cates the importance of the specific reaction conditions rehad the following properties: quired by the process of this invention to obtain superior Gravity 291 transformer oils. p pcint, O 5 The transformer 011 of Example 6 hydrogenated under Flash point, a R 285 the conditions utilized in the process of this invention but Viscosity, 5 using a naphthenic hydrocarbon distillate charge stock color, ASTM having a sulfur content of 1 weight percent does not pro Neutralization number, mg KOH/mg. v yide the improvements as obtained in the process of this Sulf pal-cent Wt m mveutlon which utilizes a naphthenic hydrocarbon dis- R f ti index 147303 tlllate having a sulfur content, below about 1 Weight percent.

EXAMPLE 7 What is claimed is: The transformer oils produced in Examples 2, 3, 4 and 39 A method for Producing a transformer oil of 5 as Well as the transformer oil charge stock of Example Perior oxidation resistance and Sludge forming Charac- 1 were subjected to various tests to determine oxidation teristics which Comprises employing as a hydroeal'boh resistance, sludge accumulation and electrical resistivity. feed, stroighi'nlh haphthehie hyfoeafbon oil distillate The oxidation test utilized herein used the method defraction having a i Cohieflt below about 1 Weight scribed in ASTM Standards on Petroleum Products and Percent and a P Point below about F: and L b i t as T f sl d Formation i i l jecting said naphthenic feed to relatively severe catalytic Transformgr Oil b i hq id i 13 hpdrogenating conditions includingapressure above about (1) 131344), 2000 p.s.i.g. and a temperature in the range of from about The sludge accumulation test utilized herein Was the 600 to about to Produce Said transformer method described in ASTM Standards on Petroleum A method for producing a transformer il which Products and Lubricants as Test for Sludge Formation Comprises relatively Severely hydfogenflthlg at a Pressure i T a f Oil (D 1314 54 above about 2000 p.s.i.g. and a temperature above about The electrical resistivity test utilized herein is an ASTM in the Presence of a Strong hydfogellating Cata- Designation; D 111694 i d Standard Method f lyst, a naphthenic distillate hydrocarbon fraction having Test for Insulation-Resistivity of Electrical Insulating Oils 3 P Point below about and a Sulfur Content f P t l O i i not substantially above about 0.7 Weight percent and The comparative results of the above tests are set forth recoverin a hydrogenated Product Comprising Said sin Table I below: former oil.

Table 1 Acid Treat- Furfural Charge ment and Refined Hydro- Hydro- Hydro- Stock, Percolaand Clay genated genated genated Ex. 1 tion, Ex. 2 Pereola- Oil, Ex. 4 Oil, Ex. 5 Oil, Ex. 6

tion, Ex. 3

Oxidation, percent wt 0.16 0. 023 0. 10 0.10 0. 055 0. 05s Sludge Accumulation:

Percent Wt. at 3 days 0. c5 0. 04 0. 0s 0. 0c 0. 005 o, 016 Percent Wt. at 7 days 0.11 0.08 0.15 0, or 0. 00a 0. 025 Percent Vv't. at 14 days. 1. 45 0.21 0. 27 0.16 0.07 0. 16 Resistivity, ohm-cm. 10 183 513 302 1310 262 The comparative results clearly demonstrate the im- 3. A method for producing a transformer oil which proved transformer oils (Example 5) obtained by the comprises severely hydrogenating in the presence of a process of this invention over transformer oils refined strong hydrogenating catalyst, a naphthenic oil distillate by conventional procedures and over another transformer 69 fraction having a sulfur content below about 1 Weight oil hydrogenated under milder hydrogenation conpercent, a flash point between about 200 F. and about ditions. The transformer oils produced by conven- 350 F. and a pour point less than about 50 F. with tional methods (Examples 2 and 3) have properties hydrogen at a temperature in the range of from about which fall within the acceptable specifications of a com- 600 to about 750 F. While maintaining a pressure during mercial transformer oil. Comparing the results of the 70 said hydrogenation step above about 2000 pounds per improved transformer oil of this invention with those of square inch and recovering a hydrogenated product comthe acceptable transformer oils, it can be readily seen prising said transformer oil. that the amount of undesirable sludge formed in the con- 4. A method for producing a transformer oil which ventional transformer oils range from about 3 to almost comprises hydrogenating a naphthenic hydrocarbon oil distillate fraction having a sulfur content below about 7 8' 1 eight percent and a pour point below about -50 F. 2,904,505 9/59 Cole. 208-264 in the presence of a hydrogenating catalyst at a liquid 2,921,025 1/60! Holm et a1 208-264 hourly space velocity from about 0.25 to about 2.0 at 2363 426 12/60 I H ld 208 211 a pressure greater than about 2000 pounds per square 935 5 5 5 1 i l et 1 203M2 4 inch anda temperature in the range of from about 625 5 33905807 9/61 7 Wasson et a 203 212 to about R 3,012,963 12/61 Archibald 208-264 3,020,228 2/62 Demeester 208-264 References Cited by the Examiner UNITED STATES PATENTS ALPHONSO D. SULLIVAN, Primary Examiner. 2,554,282 5/51 Voorhies 208-264 10 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3, 192, 153 June 29, 19

Michael T. Smilski It is hereby certified that error appears in the above numbered patent reqliring correction and that the said Letters Patent should read as correctedbelow.

Column 3, lines 26 and 4S, and column 4, line 1, for "4 1/2", each occurrence, read 4-1/2 column 5, line 1.

for "3 1/2" read 3l/2 line 25, for "mg K," second OCCI rence, read gm. n

Signed and sealed this 7th day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Allusting Officer Commissioner of Patents 

1. A METHOD FOR PRODUCING A TRANSFORMER OIL OF SUPERIOR OXIDATION RESISTANCE AND SLUDGE FORMING CHARACTERISTICS WHICH COMPRISES EMPLOYING AS A HYDROCARBON FEED, A STRAIGHT-RUN NAPHTHENIC HYDROCARBON OIL DISTILLATE FRACTION HAVING A SULFUR CONTENT BELOW ABOUT 1 WEIGHT PERCENT AND A POUR POINT BELOW ABOUT - 50*F., AND SUBJECTING SAID NAPHTHENIC FEED TO RELATIVELY SEVERE CATALYTIC HYDROGENATING CONDITIONS INCLUDING A PRESSURE ABOVE ABOUT 2000 P.S.I.G. AND A TEMPERATURE IN THE RANGE OF FROM ABOUT 600 TO ABOUT 750*F. TO PRODUCE SAID TRANSFORMER OIL. 